Tribes: David Simon is the finest anthropologist entertainment television has ever known. Just as he did when he raised his journalistic game to the level of ethnography with the non-fiction books, "Homicide" and "The Corner," so has he used prime-time drama to take viewers into urban American subcultures at a depth no other American TV producer has ever approached. Instead of police, drug dealers, dock workers, city hall, school system and newsroom employees, the tribe explored in-depth the first three episodes here is that of musicians. The series is peppered with real musicians like Elvis Costello and Dr. John. And the ensemble cast includes musicians of all sounds and stripes. Other tribes that viewers get to go backstage with include Mardi Gras Indians and small business owners trying to make in New Orleans.